Abstract Entamoeba histolytica is a protozoan pathogen and the causative agent of amoebiasis in humans. The species name (histo-: tissue; lytic-: dissolving) derives from the ability to destroy host tissues. E. histolytica trophozoites (?amoebae?) invade the large intestine, causing ulceration and can spread to other tissues (e.g., liver, lungs, brain), causing fatal abscesses. Amoebae possess contact-dependent cell-killing activity that is likely to drive tissue damage, but the mechanism was unclear. We established a new paradigm by discovering that amoebae kill by biting off and ingesting human cell fragments, which we named ?amoebic trogocytosis? (trogo-: nibble) (Ralston, et al., Nature, 2014). Building on this discovery, here we propose to delineate the unexpected contribution of trogocytosis to immune evasion. We will apply imaging flow cytometry, host and amoeba mutants, and a variety of host cell types to dissect the contribution of trogocytosis to immune avoidance in vitro, and we will use the mouse model of amoebiasis to extend these findings to pathogenesis in vivo. Beyond E. histolytica, trogocytosis has far-reaching applications to eukaryotic biology. Several microbial eukaryotes appear to use trogocytosis for cell-killing. In multicellular eukaryotes, trogocytosis is used for cell-killing, cell-cell communication and cell-cell remodeling. Trogocytosis plays roles in the immune system, in the central nervous system, and during development. Therefore, an improved understanding of the mechanism and biology of E. histolytica trogocytosis will apply both directly to the pathogenesis of amoebiasis and broadly to eukaryotic trogocytosis in general. This work is significant and high-impact as it will define a novel strategy for immune evasion and an important aspect of amoebiasis pathogenesis. Moreover, these studies apply broadly to trogocytosis as a conserved mode of eukaryotic cell-cell interaction. !